Field of the Invention
The invention relates to a gas and steam-turbine plant having a heat-recovery steam generator that is connected downstream of a gas turbine on the flue-gas side and has heating areas which are connected in a water/steam circuit of a steam turbine. The invention also relates to a method of operating such a gas and steam-turbine plant.
In a gas and steam-turbine plant, heat contained in an expanded working medium (flue gas) from the gas turbine is utilized to generate steam for the steam turbine. The heat transfer is effected in a heat-recovery steam generator, which is connected downstream of the gas turbine on the flue-gas side and in which heating areas are disposed in the form of tubes or banks of tubes. The latter in turn are connected in the water/steam circuit of the steam turbine. The water/steam circuit normally includes a plurality of pressure stages, for example two pressure stages. Each pressure stage has a preheating and an evaporator heating area.
The steam generated in the heat-recovery steam generator is fed to the steam turbine, where it expands to perform work. In this case, the steam turbine may include a number of pressure stages, which are adapted in their number and layout to the structure of the heat-recovery steam generator. The steam expanded in the steam turbine is normally fed to a condenser and condenses there. The condensate resulting during the condensation of the steam is fed again as feedwater to the heat-recovery steam generator, so that a closed water/steam circuit is obtained.
The condenser of such a gas and steam-turbine plant, like a heat exchanger, can normally be acted upon by a cooling medium, which extracts heat from the steam for the condensation. In that case, water is normally provided as the cooling medium. As an alternative, however, the condenser may also be constructed as an air condenser, to which air is admitted as the cooling medium.